Physiological and biochemical responses of the achachairu tree (Garcinia humilis) to prolonged flooding

Abstract

Flooding and waterlogging create hypoxic or anoxic soil conditions that negatively affect the physiology of wild and cultivated tropical fruit trees. The achachairu (Garcinia humilis) is a slow-growing tropical fruit tree endemic to the Bolivian Amazon region. Like many tropical trees, G. humilis is increasingly affected by flooding events that may threaten its natural and cultivated areas, but its physiological and biochemical responses to prolonged flooding have not been reported. This study assessed the physiological, biochemical, and morphological responses of G. humilis to prolonged flooding of different durations for up to 30 d Physiological variables measured included leaf gas exchange [net CO2 assimilation (A), stomatal conductance of H2O (gs), and intercellular CO2 concentration (Ci)], leaf chlorophyll index (LCI), and the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm). Antioxidant responses, such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione (GSH), glutathione reductase (GTR), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDAR), ascorbic acid (AsA), and glutathione (GSH); reactive oxygen species (ROS); and lipid peroxidation indicated by malondialdehyde (MDA) were also measured. Results indicate that G. humilis is very tolerant of flooding periods of at least 30 d, which causes approximately a 50 % reduction in net A but no measurable negative impact on other physiological variables, including LCI and Fv/Fm. Flooding caused an increase in ROS and malonaldehyde (MDA), which were countered by a robust antioxidant response that possibly contributed to improved flooding tolerance. Plants continued to grow during the flooding period, and A recovered to nearly pre-flooding levels 90 d after plants were unflooded.